Many applications require the temporary securing of a flexible sheet of material to a rotatable drum. Apparatus such as electrostatic copiers and facsimile machines as well as photographic and graphic film/print apparatus are examples of equipment requiring the supporting of a sheet of paper or film during the reading and writing processes.
Specific examples of such apparatus are found in U.S. Pat. No. 4,033,575-Fujimoro and U.S. Pat. No. 4,807,868-Lippold which show two types of automatic sheet feed and delivery apparatus employing rotatable cam and lever mechanisms for controlling clamps that hold the sheet material on the drum. The apparatus shown in the '575 patent has the disadvantage that very complex and costly apparatus is employed in the clamping arrangement that becomes difficult and expensive to operate and maintain. In the '867 patent, less complex leading and trailing edge clamps are shown for securing the sheet to the drum which relies on the spring tension of the clamps themselves for the securing force. This latter arrangement has the disadvantage of having the clamps being susceptible to centrifugal force, reducing the spring tension applied to the sheet clamps and, as a consequence, reducing the sheet holding properties of the clamp arrangement which can be a particular problem at higher rotational speeds.
It is apparent from the foregoing that there is a need for relatively simple and easy to operate and maintain apparatus for a rotating drum sheet handler that reliably retains the sheet material on the drum in the face of centrifugal forces encountered during rotation of the drum that adversely affect the clamping action of the sheet material clamps. The present invention satisfies this need.
It is therefore an object of the invention to provide a new and improved apparatus for mounting a flexible sheet of material securely onto a rotatable drum.
It is another object of the invention to provide an apparatus for supporting a flexible sheet of material securely on a rotatable drum with minimal contact to the major area of the outfacing sheet surface.
A further object of the invention is to provide an apparatus for securing a sheet of flexible material to a drum which is particularly suited for high-speed rotation of the drum.